The long-term objectives of this project are to determine the mechanisms by which several human oncoproteins contribute to the neoplastic transformation of B lineage cells through alteration of cellular proliferation and survival. In malignancies of mature B cells, the BCL2 gene is frequently overexpressed following chromosomal translocation. The BCL2 protein enhances cell survival by currently unknown mechanisms. One aim is to establish the essential components of a biochemical pathway involving BCL2 by isolating and characterizing proteins that interact with BCL2. A yeast interfactional cloning approach will continue to be employed to isolate BCL2-interacting proteins, one of which (BIP1) has recently been cloned. Structure/function studies will determine portions of BIP1 that mediate interactions with BCL2 and possibly other cellular proteins. Transfection and gene transfer studies are planned to demonstrate functional consequences to these interactions on cell survival and programmed cell death. Additional cellular protein that interact with BCL2 and BIP1 will be isolated using interfactional cloning and biochemical techniques. In a subset of B cell precursor malignancies, translocation result in fusion proteins with the features of chimeric transcription factors. Additional aims will address mechanisms by which cells. Transcriptional properties will be studied on appropriate reporter constructs to assess differences compared to respective wild type PBX and HLF proteins. Structure/function analyses will define domains essential for transcriptional activity. The E2A chimeras will be used in a variety of transformation assays including in vitro bone marrow culture and transgenic mice to establish or further characterize their oncogenic properties. Transforming and transcriptional activities will be correlated to determine molecular requirements underlying lymphoid growth control and its link to programmed cell death pathways. Interactions of transcriptional chimeras with endogenous cellular proteins and biologically relevant target genes will be studied as part of a concerted approach to define intracellular pathways for their oncogenic activity. Improved understanding of the properties of these oncoproteins will lead to important information regarding normal lymphopoiesis and may suggest new approaches for the diagnosis and treatment of lymphoid malignancies.